thunderstorms became severe as it moved east-southeast. At 8:39 PM, the National Weather Service issued a severe thunder- storm warning (see following text) for areas at and ahead of this line, including the fair- grounds (see boxed area in Fig. 3).
BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING NATIONAL WEATHER SERVICE INDIANAPOLIS IN 839 PM EDT SAT AUG 13 2011: UNTIL 945 PM EDT
AT 835 PM EDT … NATIONAL WEATH- ER SERVICE DOPPLER RADAR INDI- CATED A LINE OF SEVERE THUNDER- STORMS CAPABLE OF PRODUCING QUARTER SIZE HAIL … AND DAMAG- ING WINDS IN EXCESS OF 60 MPH. THESE STORMS WERE LOCATED ALONG A LINE EXTENDING FROM 9 MILES NORTH OF ZIONSVILLE TO GRE- ENCASTLE … AND MOVING EAST AT 25 MPH.
PRECAUTIONARY/PREPAREDNESS AC- TIONS …
SEVERE THUNDERSTORMS PRODUCE DAMAGING WIND IN EXCESS OF 60 MILES PER HOUR … DESTRUCTIVE HAIL … DEADLY LIGHTNING … AND VERY HEAVY RAIN. FOR YOUR PRO- TECTION MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF YOUR HOME OR BUSINESS. HEAVY RAINS FLOOD ROADS QUICKLY SO DO NOT DRIVE INTO AREAS WHERE WA- TER COVERS THE ROAD.
This warning was sent out approximately ten-fifteen minutes in advance of the stage collapse, and it would have been broadcast by local media via the Emergency Alert Sys- tem. To an untrained eye, it would appear that by 9:00 PM, the severe thunderstorm had not yet passed the fairgrounds, which is mostly true, but the leading edge of the storm, or outflow boundary was advanc- ing well ahead of the storm. The outflow boundary contains the highest wind gusts within most thunderstorms; one can think of this as the sting at the snake’s head. The strong outflow signature was readily appar- ent on Doppler radar velocity data, which show low-level winds by tracking ambient rain drop movement (not shown). Anoth- er suggestion of this strong outflow domi- nance is the slight bulging or bowing out of the line at 8:45 PM (Figs. 2c&d). Such analysis could be used to reconcile disputing evidence by providing a clear re- construction of the storm’s timing, impacts, and warning information, and hopefully lead to a fair outcome for all parties.
www.vtbar.org
Figure 3. National Weather Service Indianapolis, IN, severe thunderstorm warning polygon issued 8:39 PM EDT August 13, 2011. Location of stage collapse noted by white star.
Figure 4. National Weather Service Gray, Maine, radar three-hour rainfall estimates ending at 8:00 PM EDT August 7, 2008. Location of Ames Brook Drainage outlined in green and incident location noted by “X.”
Flash Flooding Example: Ames Brook Campground Fatality
On the evening of August 7, 2008, heavy rainfall caused a family to evacuate their campsite at Ames Brook Campground in Ashland, New Hampshire. As they drove across Ames Brook, their vehicle was inun- dated by high water and swept away, kill- ing a seven year-old girl. A lawsuit was filed by the family against the campground, and the defense hired the author to reconstruct
THE VERMONT BAR JOURNAL • WINTER 2012
weather conditions surrounding the inci- dent.
One of the most important parts of the analysis was to show the historical frequen- cy of the rainfall. If this event was found to be relatively common, than the camp- ground may have more responsibility to protect its campers, and thus more culpa- bility. On the other hand, if the event was shown to be very rare, then less responsi- bility may lie with the campground. Radar rainfall amount estimates from the
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The Forensic Meteorologist—“Reconstructing Weather”
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